Texas Instruments TI-2550-IV

Date of introduction:  1978 Display technology:  Fluorescent
New price:   Display size:  8
Size:  5.8" x 3.2" x 1.3"
 147 x 81 x 32 mm3
Weight:  6.7 ounces, 190 grams Serial No:  5120
Batteries:  BP4 Date of manufacture:  wk 08 year 1979
AC-Adapter:  AC-9900/H Origin of manufacture:  Italy (RCI)
Precision:   Integrated circuits:  TMC1981, TMC0999
Memories:  1 + 20 Playback    
Program steps:   Courtesy of:  Ken Meine
    Download manual:   (EU: 6.2M Bytes)

With the TI-2550-IV calculator Texas Instruments introduced a new feature into the TI-2550 series, the Playback mode known from the TI-1680. Similar to a paper printout you can scroll back up to 20 of your entries and do some corrections. The calculator looks somewhat unusual to us due to the missing ON/OFF-switch and only 24 instead of 28 keys known from the TI-2550 III.

TI-2550-IV_Back.jpg (278495 Byte)Based on its late introduction in 1978, this calculator was never a success for Texas Instruments. We assume that it was sold only in some European countries. Up to now we discovered only few calculators assembled in Italy and Turkey on the market.

TI-2550-IV_PCB.jpg (76260 Byte)
TI-2550-IV_PCB1.jpg (222317 Byte)The internal construction of the TI-2550-IV is once again completely different from the previous TI-2550 II and TI-2550 III calculators. We notice e.g. another battery pack BP4 and rather complex electronics.

TI-2550-IV_IC.jpg (151608 Byte)Dismantling the TI-2550-IV reveals indeed the electronics of the TI-1680, a TMC1981 single-chip calculator circuit supported by a TMC0999 memory chip and the BP5IC battery charger chip. All chip numbers sound familiar to us:

TMC1981: Member of the TMS1000 Microcomputer family, used e.g. in the Dataman
TMC0999: Probably a TMC0599 memory chip known from the SR-56
BP5IC: Battery charger chip used in the rechargeable battery packs BP7, BP8 and BP9

Read more about the memory operations possible with just the [M] and [MR] keys here.

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Joerg Woerner, December 5, 2001. No reprints without written permission.